Field of the Invention
The invention relates to a safety device against overpressure failure of a nuclear reactor pressure vessel in case of insufficient cooling of the core.
If the extremely improbable failure of all of the cooling devices of the reactor core is assumed in a nuclear power station in general, and in a pressurized-water reactor nuclear power station in particular, there is a risk of the reactor core overheating. In a pressurized-water nuclear power station, an unacceptable overpressure in the primary circuit is prevented by the pressurizer system containing spray and pressure relief devices. A pressurizer relief tank serves to condense the steam blown off upon opening of the pressurizer valves, relief valves and safety valves and of the volume control system safety valves. The pressurizer relief tank is filled with water to about two thirds, above which there is a nitrogen cushion. In the case of pressurized-water reactors, the primary circuit is at a pressure of, e.g., 158 bar (normal operation).
German Published, Non-Prosecuted Application DE 35 26 377 A1, corresponding to U.S. Pat. No. 4,777,013, describes a high-temperature reactor with a reactor pressure vessel and a safety valve, being constructed as a spring valve, for limiting the pressure in the reactor pressure vessel in case of core heat-up accidents. The reactor pressure vessel is lined on its inside with a liner connected to a liner-cooling system. The valve spring of the safety valve is formed of a material having an elastic force which decreases with increasing temperature. When the safety valve is open, the valve spring is exposed to outflowing gas and is connected to the liner-cooling system for the purpose of cooling.
The invention is based on the concept of substantially reducing the popping or blow-off response pressure in the cooling circuit of a nuclear reactor as a function of temperature, especially in the primary circuit of a pressurized-water reactor, so that in the very unlikely case of the reactor core overheating, the primary-circuit pressure is automatically reduced to values below 30 bar.